[PATCH v2 3/3] posix: New Linux posix_spawn{p} implementation

[Adhemerval Zanella]

On 03-02-2016 09:06, Torvald Riegel wrote:
> On Tue, 2016-02-02 at 11:31 -0200, Adhemerval Zanella wrote:
>>
>> On 02-02-2016 11:05, Florian Weimer wrote:
>>> On 02/01/2016 05:21 PM, Adhemerval Zanella wrote:
>>>
>>>> +  new_pid = CLONE (__spawni_child, STACK (stack, stack_size),
>>>> +		   CLONE_VM | CLONE_VFORK | SIGCHLD, &args);
>>>
>>> Does this set up new per-thread variables?  Otherwise, errno in the
>>> parent and child will be same and the code still has races.
>>>
>>> Florian
>>>
>>
>> Could you elaborate? In my understanding there is no requirement of
>> using CLONE_SETTLS to avoid races: CLONE_VFORK will suspend the 
>> calling process and even with child using the same TLS namespace as
>> the parent there will be no concurrent access between them.
> 
> Whatever you agree on eventually, it sounds as if this should be
> documented as part of the concurrency notes for this function.
> 

I think it is worth to comment internally on the function implementation
about the CLONE_VFORK synchronization, but since it is transparent
to user (the function will either spawn a new process or fails and it can
be either through a syscall, {v}fork/exec or any other mechanism),
I do not see why expose these implementation details explicit.